One form of edge filter is described in the Davis et al U.S. Pat. No. 3,829,014 issued Aug. 13, 1974 and entitled "Fuel Injector Having Self-Cleaning Filter". In that design, a filter sleeve is inserted in the valve chamber adjacent the valve guide at a location between the fuel inlet and the valve tip.
Cylindrical edge filters also have been provided within the inlet stem of the fuel injector and have been retained therein by providing them with a longitudinal end slot. A roll pin forced into the slot cams the slotted end outwardly into firm engagement with the stem. This design not only requires multiple parts and is expensive to install but also permits damage to the edge filter by excess flexure of the slotted end which tends to crack the case hardened outer surface of the edge filter. In order to avoid the excess flexure problem, substantially closer tolerances are required on both the bore and the filter and these tolerances must be closely controlled.